Flat panel displays have rapidly become ubiquitous in various markets, and are now commonly utilized in a variety of appliances, televisions, computers, cellular phones, and other electronic devices. One example of a commonly used flat panel display is the thin film transistor (TFT) liquid crystal display (LCD), or TFT-LCD. A typical TFT-LCD contains an array of TFTs each controlling the emission of light from a pixel or sub-pixel of an LCD. FIG. 1A depicts the cross-section of a conventional TFT 100 as might be found in a TFT-LCD. As shown, the TFT 100 includes a gate electrode 105 formed on a glass substrate 110. A gate insulator 115 electrically insulates the gate electrode 105 from overlying conductive structures. An active layer 120, typically composed of amorphous silicon, conducts charge between a source electrode 125 and a drain electrode 130, under the electrical control of gate electrode 105, and the conducted charge controls the operation of the pixel or sub-pixel connected thereto (not shown). A source/drain insulator 132 electrically isolates the source electrode 125 from the drain electrode 130 and protectively seals the TFT 100. As shown, each of the gate electrode 105, source electrode 125, and drain electrode 130 typically include a barrier metal layer 135 and a metal conductor layer 140 thereover. The barrier 135 provides good adhesion between the conductor 140 and the underlying glass and/or silicon and reduces or prevents diffusion therebetween.
Over time, LCD panel sizes have increased and TFT-based pixel sizes have decreased, placing increasingly high demands on the conductors within the TFT-LCD structure. In order to decrease the resistance in the conductors and thereby increase electrical signal propagation speeds in the TFT-LCD, manufacturers are now utilizing low-resistivity metals such as copper (Cu) for the conductors 140 within the display. Metals such as molybdenum (Mo), titanium (Ti), or molybdenum-titanium alloys (Mo—Ti) have been utilized for barriers 135 underlying Cu conductors 140; however, these metals suffer from one or more deficiencies that limit the performance of the TFT-LCD and/or present difficulties in the fabrication process for the TFT-LCD. For example, some conventional barriers 135 have relatively high resistivity and therefore compromise the overall conductivity of the electrodes. Furthermore, as shown in FIG. 1B, during the etching of electrodes such as gate electrodes 105, either a residue 145 (of one or both electrode materials) or etch discontinuities 150, e.g., stepped or nonlinear profiles (caused by non-uniform etch rates of the two different electrode materials), may result.
Similarly, touch-panel displays are becoming more common in electronic devices, and they may even be utilized in tandem with TFT-LCDs. A typical touch-panel display includes an array of sensors arranged in rows and columns and that sense a touch (or close proximity) of, e.g., a finger, via capacitive coupling. FIG. 2A schematically depicts an exemplary sensor array 200 for a touch-panel display that includes multiple conductive column sensors 210 that are interconnected to form columns 220, as well as multiple conductive row sensors 230 that are interconnected to form rows 240. The sensors 210, 230 are formed over a substrate 250 and are electrically coupled to a processor 260 that both senses the changes in capacitive coupling that represent “touches” and provides these signals to other electronic components within a device (e.g., a computer or mobile computing device that incorporates a touch screen). The sensors 210, 230 may be formed of a transparent conductor such as indium tin oxide (ITO), and the substrate 250 may be glass or any other suitably rigid (and/or transparent) support material.
FIG. 2B depicts a magnified perspective view of a point within the sensor array 200 where the interconnected column sensors 210 intersect the interconnected row sensors 230. In order to avoid electrical shorting between the columns 220 and the rows 240 (see FIG. 2A), the interconnections between column sensors 210 are isolated from the underlying or overlying row sensors 230. For example, as shown in FIG. 2B, an insulator layer 270 is disposed between the column 220 of column sensors 210 and a conductive interconnect (or “bridge”) 280 that electrically connects the row sensors 230 within a row 240. As shown in FIG. 2C, the interconnects 280 are typically composed of an Al conductive layer 290 with an overlying barrier or capping layer 295 that is typically composed of Mo, Ti, or Mo—Ti. The capping layer 295 helps to prevent diffusion from the conductive layers 290 and protects conductive layers 290 from corrosion during processing and product use. The capping layer 295 may also improve adhesion to overlying layers. However, as described above for TFT-LCDs, the metals conventionally used for the capping layer 295 metals from one or more deficiencies that limit performance and/or present difficulties in the fabrication process. For example, the capping layers 295 may have relatively high resistivity and therefore compromise the overall conductivity of the interconnects 280, degrading electrical performance. Furthermore, as shown in FIG. 2D, during the etching of the interconnects 280, either a residue 296 (of one or both of conductive layer 290 or capping layer 295) or etch discontinuities 297, e.g., stepped or nonlinear profiles (caused by non-uniform etch rates of the two different materials), may result.
In view of the foregoing, there is a need for barrier and/or capping metal layers for electronic devices such as TFT-LCDs and touch-panel displays that provide excellent adhesion to underlying substrates, prevent diffusion of the conductor metal into nearby layers, protect the conductor metal from corrosion, and are uniformly etched with the underlying or overlying conductor metals during fabrication.